1. Field of the Invention
The present invention relates to a source driver and an internal data transmission method thereof, and more particularly to a source driver and an internal data transmission method adapted for use with a dot inversion driving method.
2. Description of Related Art
As an important component of a thin film transistor liquid crystal display (TFT-LCD), a source driver is responsible for converting the digital signals required for image displaying into analog signals and outputting the converted signals to every sub-pixel, also referred to as a dot, of a TFT-LCD.
FIG. 1 is a structural block diagram of a conventional source driver 100. Referring to FIG. 1, a conventional source driver 100 receives a plurality of data signals 110 and outputs a plurality of analog signals with N output channels, Y1 through YN. The conventional source driver 100 includes a shift register 101, a line latch 102, a level shifter 103, a digital-to-analog converter (DAC) 104, and an output buffer 105. Those skilled in the art should understand that in a conventional source driver 100, the shifter register 101 allocates the data signals 110 to output channels Y1 through YN; then the line latch 102 provisionally stores the data signals 110; and the level shifter 103 amplifies the data signals 110; then the DAC 104 converts the amplified data signals 110 into analog signals; and finally the output buffer 105 outputs the analog signals.
In a TFT-LCD, for avoiding polarization of liquid crystals used as the material for display control, alternating current (AC) voltages accompanying with inversion driving methods such as line inversion, column inversion, and dot inversion must usually be used for driving. FIG. 2 depicts the driving polarity of the sub-pixels of the respective frame T and frame T+1 for a TFT-LCD for illustrating a dot inversion driving method, in which the symbol “+” represents positive driving polarity and symbol “−” represents negative driving polarity. As illustrated in FIG. 2, the so-called dot inversion means that each sub-pixel has opposite polarity with adjacent sub-pixels, irregardless of whether in horizontal or perpendicular direction, and that all the sub-pixels have their polarities inverted at the next frame.
Although a dot inversion driving method has many advantages, it unfortunately consumes relatively more power than others. Referring to FIG. 3, a source driver 301 outputs analog signals to the sub-pixels, SP0 through SP3, of a single scan line SL of a pixel array 303 via an output buffer 302 and data lines DL0 through DL3. Because current large-sized TFT-LCD panel usually adopts a direct current (DC) common voltage (Vcom) design, voltages of positive polarity higher than the common voltage Vcom and voltages of negative polarity lower than the common voltage Vcom are thus possible. For example, the data lines DL0 and DL2 output voltages respectively have polarities as positive, negative, and positive, while the data lines DL1 and DL3 output voltages respectively have polarities as negative, positive, and negative. Whenever upon entering into next scan line or upon a frame is shifted to the next frame, data lines DL0 through DL3 must have their polarities inverted; therefore, the source driver 301 has to provide a swing voltage Vswing which is about twice that of the common voltage Vcom. The higher the Vswing, the more the power consumption becomes. In consistent with increasing panel size, increasing in resolution, and introduction of wider viewing angle technologies such as the in-plane switching (IPS) and multi-domain vertical alignment (MVA), all of which require higher power consumption. Thus the disadvantage of power consumption of the dot inversion driving method becomes even more apparent.
In addition, another disadvantage of the conventional technology is that the DAC has to output voltages of both positive polarity and negative polarity. Being limited by a threshold voltage, an n-channel metal oxide semiconductor field effect transistor (NMOS) is not able to be used for transferring high voltage; whereas, a p-channel metal oxide semiconductor field effect transistor (PMOS) is not able to be used for transferring a low voltage. Therefore, the DAC has to adopt a complementary metal oxide semiconductor field effect transistor (CMOS), which is relatively larger in size and higher in cost.